1. Field of the Invention
The present invention relates to a belt tension adjustment mechanism and an image forming apparatus which includes the belt tension adjustment mechanism.
2. Description of Related Art
Conventionally, there have been known tandem type image forming apparatuses each of which includes image processing units for a plurality of colors such as Y (yellow), M (magenta), C (cyan) and K (black), forms monochrome toner images of respective colors on photoreceptors in the respective image processing units and sequentially transfers the monochrome toner images of the respective colors to form a color image on sheets of paper, for example.
Generally, an intermediate transfer belt for sequentially conveying the monochrome toner images is provided with a predetermined tension. When a thick sheet (heavy paper) having a large thickness is conveyed through a nip section which is formed between the intermediate transfer belt and a secondary transfer roller for transferring (secondary transfer) color toner images on the conveyed sheet, an impact caused by the contact with the thick sheet transfers to the intermediate transfer belt, and the tension provided to the intermediate transfer belt is changed. When the tension provided to the intermediate transfer belt is changed, positions of the respective color monochrome toner images are shifted when they are superposed on each other, which leads to a color deviation.
Thus, in order to minimize the change in tension applied to the intermediate transfer belt, there is disclosed a technique to compensate for the change in vector relationship between the tension of intermediate transfer belt and the load in vertical direction with arms which are supported to be rotatable and stretchable to have a tensile force and a tensioner mechanism which connects the supported arms to each other so as to be rotatable (for example, see Japanese Patent Application Laid-Open Publication No. 2002-6573).
However, the above technique of Japanese Patent Application Laid-Open Publication No. 2002-6573 possibly cannot respond to a rapid change in the tension due to the inertia action of link mechanism to constrain the motion. In addition, there is a large dead force generated at the rotation supporting point with respect to the load which is applied to the intermediate transfer belt by the tensioner mechanism. Thus, the operation of tensioner mechanism is possibly disturbed by the frictional force. As described above, the technique described in Japanese Patent Application Laid-Open Publication No. 2002-6573 has a problem that it is difficult to maintain the tension applied to the intermediate transfer belt to be constant due to the disturbance by inertia force and frictional force.